Process for coating glass

ABSTRACT

A process for the production of durable photocatalytically active self-cleaning coating on glass by contacting a hot glass surface with a fluid mixture of titanium chloride, a source of oxygen and a tin precursor. The coating preferably comprises less than 10 atom % tin in the bulk of the coating and preferably there is a greater atomic percent tin in the surface of the coating than there is in the bulk of the coating. Preferably, the coating is durable to abrasion and humidity cycling.

TECHNICAL FIELD

The present invention relates to a process for the production of adurable photocatalytically active self-cleaning coated glass. Inparticular the present invention relates to a process for depositing adurable, photocatalytically active self-cleaning coating of titaniumoxide containing tin on the surface of a glass substrate. The presentinvention also relates to a durable, photocatalytically active coatedglass having a coating comprising titanium oxide containing tin.

BACKGROUND ART

It is known to deposit thin coatings having one or more layers with avariety of properties on to glass substrates. One property of interestis photocatalytic activity which arises by photogeneration, in asemi-conductor, of a hole-election pair when the semi-conductor isilluminated by light of a particular frequency. The hole-electron paircan be generated in sunlight and can react in humid air to form hydroxyand peroxy radicals on the surface of the semi-conductor. The radicalsoxidise organic grime on the surface which both cleans the surface andincreases the hydrophilic properties (i.e. wettability) of the surface.A hydrophilic surface is beneficial because water will wet the surfacebetter, making the surface easier to clean with water containing littleor no detergent. In addition, water droplets will spread over thesurface reducing the distracting visual effects of rain or spray. Thus,photocatalytically active coated glass has a use in self-cleaning glassfor windows.

Titanium dioxide may be deposited on to glass to form a transparentcoating with photocatalytic properties. In WO 98/06675 a chemical vapourdeposition process is described for depositing titanium oxide coatingson hot flat glass at high deposition rate. In EP 901 991 A2 aphotocatalytically active titanium oxide coating deposited by DVD isdisclosed.

Mixed oxide coatings of titanium with other metals are known. In GB 2275 691 a glass substrate having a pyrolytically formed coating isdescribed, characterised in that the coating comprises tin oxide andtitanium oxide. The coating may be formed by contacting a hot glasssubstrate with a titanium containing precursor being the reactionproduct of octyleneglycol titanate and acetylacetonate together with atin-containing coating precursor, for example tin dibutyl/diacetate.Similar mixed titanium/tin oxide coatings are disclosed in GB 2150044and U.S. Pat. No. 4,687,687.

In WO 95/15816 sol gel processes for producing photocatalytically activetitanium oxide coatings which contain tin oxide particles are described.

In WO 98/10186 it is stated that a photocatalytically active coating maycontain one other type of mineral material for example an oxide ofsilicon (or mixture of oxides) of titanium, tin, zirconium or aluminium.It has been suggested in WO98/10186 that mixed oxides coatingscontaining titanium oxide or titanium oxide coatings may haveadvantageous optical properties for example by lowering the refractiveindex of the coating.

A problem arises with known photocatalytically active coatings based ontitania in that the durability of the coating, especially to abrasion,may be poor. This is especially problematic because such coatings willoften be used for their self-cleaning property and this use requires thecoating to be on the outside surface of e.g. glazings where the coatingmay be particularly prone to abrasion.

The applicants have discovered that this problem may be addressed bydepositing a titania coating containing tin on hot glass from a fluidcontaining a titanium precursor and a tin precursor.

DISCLOSURE OF INVENTION

The present invention accordingly provides a process for the productionof a durable photocatalytically active self-cleaning coated glasscomprising contacting the surface of a hot glass substrate with a fluidmixture comprising titanium chloride, a source of oxygen and a tinprecursor thereby depositing a tin containing titanium oxide coating onthe surface of the glass substrate.

Coated glasses produced by the process of the invention havesurprisingly high durability, both to abrasion (as determined forexample, by the European standard abrasion test as described in BritishStandard BS EN 1096 (Part 2, 1999)), and to temperature cycling in ahumid atmosphere. Preferably, the coated glass is durable to abrasionsuch that the coated surface retains a photocatalytic activity afterbeing subjected to 500 strokes of the European standard abrasion test.

Preferably, at least part of the fluid mixture contacts the surface ofthe glass substrate by flowing over the surface of the glass substrateor, more preferably, by flowing over the surface of a glass substratewhich is moving relative to the coating apparatus.

The preferred titanium chloride comprises titanium tetrachloride becauseit is relatively cheap, obtainable in pure form and volatile (allowinggood carry over to the glass surface). However, generally any titaniumprecursor having a chloro substituent may be used in the process of theinvention.

Preferably, the tin precursor comprises a tin halide (i.e. a tincompound having a halo substituent), more preferably the tin precursorcomprises a tin chloride and most preferably the tin precursor comprisesdimethyl tin dichloride ((CH₃)₂ Sn Cl₂, DMT) or tin tetrachloride (SnCl₄). This is advantageous because these tin precursors are relativelycheap in bulk, obtainable in pure form and provide good carryover to theglass surface during deposition of the coating.

The source of oxygen preferably comprises an ester, especially acarboxylic acid ester. Usually, the ester will comprise a C₁ to C₄acetate because these esters are relatively volatile providingrelatively efficient incorporation of the ester in a carrier gas stream(this may be done, for example, by bubbling the carrier gas through theliquid ester). Most preferably the ester comprises ethyl acetate whichis cheap and has low toxicity.

Usually, the glass substrate will comprise a soda-lime-silicate glasssubstrate.

If the glass substrate comprises a soda-lime-silicate glass substrate oranother glass substrate comprising alkali metal ions, the process of theinvention preferably further comprises depositing an alkali metal ionblocking underlayer on the surface of the glass substrate beforedepositing the coating of titanium oxide containing tin. This isadvantageous because an alkali metal ion blocking underlayer reducesmigration of alkali metal ions from the glass substrate into thephotocatalytically active coating which could reduce the photocatalyticactivity of the coating and/or generate haze. Preferred alkali metal ionblocking underlayers comprise a silicon oxide layer (which has similarretractive index to the glass substrate and so has little effect on theoptical properties of the coated glass) or a double layer of tin oxideand silicon oxide. Alternatively, other alkali metal ion blocking layersknown in the art may be used if desired.

The photocatalytically active coating may be deposited using spraydeposition (in which the fluid mixture comprises liquid droplets) orchemical vapour deposition (CVD, in which the fluid mixture comprises agaseous mixture). The preferred deposition process is CVD, thus,preferably the fluid mixture comprises a gaseous mixture.

Usually, the hot glass substrate will be at a temperature in the rage500° C. to 750° C. which has been found in practice to be an especiallysuitable temperature range for depositing durable photocatalyticallyactive coatings comprising titania.

At temperatures much lower than this the photocatalytic activity ofcoatings based on titania begins to drop off. At higher temperaturessome kinds of glass (including soda-lime-silicate glass) may begin tosoften. Preferably the hot glass substrate is at a temperature in therange 570° C. to 650° C.

The process will usually be performed at substantially atmosphericpressure.

It is advantageous if the process is performed during the float glassproduction process because this is especially suitable for producinglarge volumes of coated glass. In this case the process is preferablyperformed in the float bath.

In preferred embodiments of the invention the amount of tin in the bulkof the tin containing titanium oxide coating is below about 10 atom %(as determined by X-ray photoelectron spectroscopy, XPS), preferablybelow about 5 atom % and more preferably below about 2 atom %. At higheramounts of tin, there may be a reduction in photocatalytic activity ofthe coated glass. The amount of tin in the bulk of the coating willusually be above about 0.05 atom %. Thus, preferably the amount of tinin the bulk of the coating is in the range 0.05 atom % to 10 atom %,more preferably in the range 0.05 atom % to 5 atom % and most preferablyin the range 0.05 atom % to 2 atom %. Thus, in another aspect, thepresent invention provides a process for depositing a tin containingtitanium oxide coating on the surface of a hot glass substratecomprising contacting the surface of the glass substrate with a fluidmixture comprising a titanium precursor, a source of oxygen and a tinprecursor characterised in that the amount of tin in the bulk of the tincontaining titanium oxide coating is below 10 atom %. The tin content ofthe coatings appears to provide or contribute to the surprisingly highdurability of coatings deposited according to the invention.

The applicants have unexpectedly discovered that in tin containingtitanium oxide coatings deposited according to the invention, there is agreater atomic percent tin in the surface of the tin containing titaniumoxide coating than there is in the bulk of the coating. This may beadvantageous in providing greater increase in durability for arelatively small amount of tin since durability to abrasion, humidity orother factors is likely to depend most on the surface of a coating. Thesurface of the coating normally means approximately 10% of the thicknessof the coating in terms of the total coating thickness.

Preferably, the atomic percent tin in the surface of the tin containingtitanium oxide coating is at least twice that in the bulk of thecoating.

The present invention provides in a further aspect a durable,photocatalytically active coated glass comprising a glass substratehaving a coating comprising tin containing titanium oxide, the amount oftin in the bulk of the coating being below 10 atom %. The atomic percenttin in the surface of the coating is preferably at least twice that inthe bulk of the coating, and is preferably above 0.05 atom %.

Coated glasses according to the invention have uses in many areas ofglass use including as glazings in buildings (either in single glazing,multiple glazing or laminated glazing) or in vehicles (either inlaminated glazings or otherwise).

Preferably, coated glasses according to the invention will have valuesof visible reflection measured on the coated side of 25% or lower, morepreferably of 20% or lower and most preferably of 15% or lower.

Coated glasses according to the invention are photocatalytically activewhich is advantageous because the amount of contaminants (includingdirt) on the coated surface of the photocatalytically active coatedsubstrate will be reduced if the surface is illuminated by UV light(including sunlight).

Preferably, the coated glass has a static water contact angle (on thecoated side) of 20° or lower. The static water contact angle is theangle subtended by the meniscus of a water droplet on a glass surfaceand may be determined in a known manner by measuring the diameter of awater droplet of known volume on a glass surface and calculated using aniterative procedure. Freshly prepared or cleaned glass has a hydrophilicsurface (a static water contact angle of lower than about 40° indicatesa hydrophilic surface), but organic contaminants rapidly adhere to thesurface increasing the contact angle. A particular benefit of coatedglasses of the present invention is that even if the coated surface issoiled, irradiation of the coated surface by UV light of the rightwavelength will reduce the contact angle by reducing or destroying thosecontaminants. A further advantage is that water will spread out over thelow contact angle surface reducing the distracting effect of droplets ofwater on the surface (e.g. from rain) and tending to wash away any grimeor other contaminants that have not been destroyed by the photocatalyticactivity of the surface.

Preferably, the coated glass has a haze of 1% or lower, which isbeneficial because this allows clarity of view through a transparentcoated substrate.

The invention is further illustrated by the following Examples, in whichgas volumes are measured at standard temperature and pressure unlessotherwise stated. The thickness values quoted for the layers weredetermined using high resolution scanning electron microscopy (SEM)and/or Xray photoelectron spectroscopy (XPS) depth profiling. XPS wasalso used to provide information on the surface and bulk elementalcomposition of the coatings.

The transmission and reflection properties of the coated glasses weredetermined using a Hitachi U—4000 spectrophotometer. The a, b and L*values mentioned herein of the transmission and/or reflection colours ofthe glasses refer to the CIE Lab colours. The visible reflection(measured on the coated side unless otherwise stated) and visibletransmission of the coated glasses were determined using the D65illuminant and the standard CIE 2° observer in accordance with the ISO9050 standard (Parry Moon airmass 2) The haze of the coated glasses wasmeasured using a WYK—Gardner Hazeguard+haze meter.

The photocatalytic activity of the coated glasses was determined fromthe rate of decrease of the area of the infrared peaks corresponding toC-H stretches of a stearic acid film on the coated surface of the glassunder illumination by UVA light or sunlight. The stearic acid film wasformed on samples of the glasses, 7–8 cm square, by spin casting 20 μlof a solution of stearic acid in methanol (8.8×10⁻³ mol dm⁻³) on thecoated surface of the glass at 2000 rpm for 1 minute. Infra red spectrawere measured in transmission, and the peak height of the peakcorresponding to the C-H stretches (at about 2700 to 3000 cm⁻¹) of thestearic acid film was measured. The photocatalytic activity is expressedin this specification as t_(90%) (in units of min) which is the time ofUV exposure taken to reduce the peak height by 90% (i.e. down to 10% ofits initial value). For measurement of photocatalytic activity, thecoated side of the glass was illuminated with a UVA lamp (UVA-351 lampobtained from the Q-Panel Co., Cleveland, Ohio, USA) having a peakwavelength of 351 nm and an intensity at the surface of the coated glassof approximately 32 W/m² or by sunlight outside on a clear sunny day inJune at Lathom, Lancashire, England.

The static water contact angle of the coated glasses was determined bymeasuring the diameter of a water droplet (volume in the range 1 to 5μl) placed on the surface of the coated glass as produced, or afterirradiation of the coated glass using the UVA 351 lamp for about 2 hours(or as otherwise specified).

Abrasion testing of the coated glass was in accordance with BS EN 1096,in which a sample of size 300 mm×300 mm is fixed rigidly, at the fourcorners, to the test bed ensuring that no movement of the sample ispossible. An unused felt pad cut to the dimensions stated in thestandard (BS EN 1096 Part 2 (1999)) is then mounted in the test fingerand the finger lowered to the glass surface. A load pressure on the testfinger of 4N is then set and the test started. The finger is allowed toreciprocate across the sample for 500 strokes at a speed of 60strokes/min±6 strokes/min. Upon completion of this abrasion the sampleis removed and inspected optically and in terms of photocatalyticactivity.

Humidity testing of the coated glasses comprised temperature cycling thecoated glass from 35° C. to 75° C. at 100% relative humidity.

In Examples 1 to 10 coatings were deposited on stationary glass samplesby chemical vapour deposition.

In Examples 11 to 59 and Comparative Examples A to D, a ribbon of floatglass was coated with a two-layer coating as the ribbon advanced overthe float bath during the float glass production process. The glassribbon was coated at the edge across a width of approximately 10 cm.

Layer 1 (the first layer to be deposited on the glass) was a layer ofsilicon oxide. Layer 1 was deposited by causing a gaseous mixture ofcoating precursors to contact and flow parallel to the glass surface inthe direction of movement of the glass using coating apparatus asdescribed in GB patent specification 1 507 966 (referring in particularto FIG. 2 and the corresponding description on page 3 line 73 to page 4line 75).

Layer 2 (the second layer to be deposited) was a layer comprisingtitanium dioxide. Layer 2 was deposited by combining separate gasstreams comprising titanium tetrachloride in flowing nitrogen carriergas, ethyl acetate (EtOAc) in flowing nitrogen carrier gas, tintetrachloride in flowing nitrogen or dimethyl tin dichloride (DMT) inflowing nitrogen and a bulk flow of nitrogen into a gaseous mixture andthen delivering the gaseous mixture to the coating apparatus where itcontacted and flowed parallel to the glass surface. Titaniumtetrachloride, tin tetrachloride or DMT and ethyl acetate were entrainedin separate streams of flowing nitrogen carrier gas by passing nitrogenthrough bubblers.

Table 1 describes the general deposition conditions used for the seriesof Examples and Comparative Examples, 11 to 18, 19 to 24, 25 to 59 and Ato D.

In Examples 60 to 66, two-layer coatings were applied by on line CVD toa float glass ribbon across its full width of approximately 132 inches(3.35 m) in the float bath during the float glass production process.

The two layer coating consisted of a silicon oxide layer deposited firston the float glass ribbon and tin containing titanium oxide layerdeposited on to the silicon oxide layer.

Titanium tetrachloride (TiCl₄) and ethyl acetate were entrained inseparate nitrogen carrier gas streams. For the evaporation of TiCl₄ athin film evaporator was used. The TiCl₄ and ethyl acetate gas streamswere combined to form the gaseous mixture used to deposit the titaniumoxide layer. This mixing point was just prior to the coater.

Table 2 describes the general deposition conditions used for Examples 60to 66. In Table 2, slm means standard liters per minute and sccm meansstandard cc per minute.

TABLE 1 Examples 25 to 59 Examples Examples Comparative 11 to 18 19 to24 Examples A to D Linespeed 135 m/hr 150 m/hr 150 m/hr GlassTemperature at ~630° C. ~630° C. ~630° C. TiO₂ Coater Glass Temperatureat   710° C.   725° C.   695° C. silica coater Silica UndercoatConditions SiH₄  24 cc/min  80 cc/min  80 cc/min N₂  8 l/min  8 l/min  8l/min C₂H₄ 144 cc/min 480 cc/min 240 cc/min O₂  48 cc/min 160 cc/min  80cc/min TiO₂ Conditions TiCl₄ Bubbler    50° C.   50° C.   50° C.Temperature N₂ to TiCl₄ Bubbler 125 cc/min 175–200 125–175 cc/min cc/minEtOAc Bubbler    35° C.    35° C.    35° C. Temperature N₂ to EtOAcBubbler 125 cc/min 175–200  90–210 cc/min cc/min Bulk N₂  10 l/min  10l/min  10 l/min Precursors Used SnCl₄ SnCl₄ SnCl₄ or DMT

TABLE 2 Examples 60 to 66 Linespeed 477 inches/min (727 m/hr) GlassTemperature at TiO₂ Coater 680° C.–700° C. Silica Undercoat Conditions(at each of two coaters, temperatures approximately 721° C. and 690° C.)SiH₄  2.3 slm N₂  285 slm He  250 slm C₂H₄   12 slm O₂   8 slm TiO₂Topcoat Conditions TiCl₄   10 sccm EtOAc 26.7 sccm Bulk He  300 slm BulkN₂  300 slm DMT Precursor 1.5 g/min to 4 g/min

Typical conditions for delivery of the tin precursors from bubblers forthe Examples are described in Table 3.

TABLE 3 Flow rates of Bubbler Bubbler Nitrogen Precursor DeliveryTemperature carrier gas Dimethyltin Blow approx. 140° C. 0–250Dichloride- nitrogen cc/min DMT through molten solid Tin (IV) Blowapprox. 70° C.  0–700 Chloride- nitrogen cc/min SnCl₄ through liquid

EXAMPLES 1 TO 10

In Examples 1 to 10, coatings having a two layer alkali ion blockingcoating (comprising a tin oxide layer at the glass surface and a silicalayer on the tin oxide layer) were deposited on to stationary glasssubstrates using a laboratory CVD reactor. Titania coatings weredeposited using bubblers containing TiCl₄ and ethyl acetate (EtOAc) at aTiCl₄:EtOAc molar ratio of about 1:3. The deposition conditions were setso as to give 12%–16% visible reflection. General deposition conditionsused for Examples 1 to 10 are described in Table 4.

TABLE 4 TiCl₄ Bubbler  65° N₂ to TiCl₄ 50 to 200 cc/min TemperatureBubbler EtOAc Bubbler  45° N₂ to EtOAc 75 to 200 cc/min TemperatureBubbler Substrate Temperature 660° C. Bulk N₂ 8.5 l/min (SusceptorReading) Temperature of 180– Coating Period 10–15 seconds Delivery Lines200° C.

Examples 1 to 10 were deposited using a SnCl₄ delivery range of 0 to 120cc/min nitrogen to the SnCl₄ bubbler (corresponding to about 0–0.4g/min).

The specific deposition conditions for Examples 1 to 10 are described inTable 5 together with t_(90%) for each of the deposited coatings. Therewas appreciable scatter in the measurements of t_(90%). Some of thisscatter can be explained by a varying film thickness caused byvariations in the deposition conditions (e.g. a SnCl₄ bubblertemperature of lower than 35° C. and modified carrier gas flows to TiCl₄and EtOAc bubblers).

XPS depth profiling indicated the coatings to be approximately 700 Åthick. Tin was detected throughout the containing coatings at a level of0.3 atom. % for coatings deposited at 0.08 g/min SnCl₄.

TABLE 5 N₂ Flow Rate to Bubbler Example TiCl₄ (cc/min) EtOAc (l/min)SnCl₄ (cc/min) t_(90%) (min) 1 100 130 20 62 2 140 140 20 55 3 200 20050 90 4 100 100 20 98 5 120 100 120 123 6 140 140 20 48 7 50 100 50 80 850 100 50 84 9 60 100 60 151 10 75 75 75 55

EXAMPLE 11 TO 18

Examples 11 to 18 were deposited by on line CVD during the float glassproduction process, at a TiCl₄:EtOAc molar ratio of 1:3 and at arelatively low precursor flow (0–0.4 g/min SnCl₄). All coatings weredeposited on to the silica undercoat and were optimised to give 12–16%visible reflection. The general coating conditions were as described inTable 1 above, the specific coating conditions for each of Examples 11to 18 are described in Table 6 together with t_(90%), the visiblereflection and the contact angle (static water contact measured afterexposure to ultraviolet light (UVA lamp).

TABLE 6 Nitrogen carrier gas flow rates to bubbler Visible TiCl₄ EtOAcSnCl₄ Reflection Contact Example (cc/min) (cc/min) (cc/min) t_(90%)(min) (%) Angle (°) 11 150 150 20 50.5 17.27 29 12 150 150 40 60 18.1614.3 13 150 150 60 127.5 18.85 18.7 14 150 150 80 111 19.26 12.1 15 150150 100 110 19.19 19.2 16 110 110 100 103 13.64 10.6 17 110 110 50 67.513.24 12.9 18 110 110 20 77 13.4 22.2

The coatings of Examples 11 to 18 passed a salt spray test, remainingunchanged after 830 hours. Humidity testing of the coatings for Examples11 to 19 was carried out, the coatings remained unchanged after 200cycles (the maximum number of cycles performed). In contrast, undopedtitania coatings deposited under similar conditions survived only 17cycles of the humidity test before failing at the SiO₂/TiO₂ interface.

Abrasion testing on the Examples 11 to 18 showed that tin containingtitania coatings were more robust than the undoped TiO₂ (to visualexamination).

EXAMPLES 19 TO 24

Examples 19 to 24 were deposited by on line CVD during the float glassproduction process as described in Table 1 above at a relatively highprecursor flow (0–2.8 g/min SnCl₄). The specific coating conditions foreach of Examples 19 to 24 are described in Table 7. The static watercontact angle before and after UVA exposure (for approximately 2 hours,the contact angle after UVA exposure is in brackets), t_(90%) using theUVA lamp and t_(90%) using sunlight are described in Table 8.

TABLE 7 N₂ to TiCl₄ N₂ to EtOAc N₂ to SnCl₄ Example (cc/min) (cc/min)(cc/min) 19 175 175 25 20 175 175 50 21 175 175 75 22 175 175 300 23 175175 500 24 175 175 700

TABLE 8 Contact angle before t_(90%) t_(90%) Example (after) UVAexposure (min) UVA (min) sunlight 19 43.4 (3.6)  95 129.5 20 17.8 (7)  105.5 221 21 28.8 (3.6)  165.5 262.5 22 40.9 (11.5) 116 230 23   4(3.3)  102 154 24 7.6 (4.5) 139 181.5

The haze, visible transmission, visible reflection and the transmissionand reflection colours of Examples 19 to 24 are described in Table 9.

TABLE 9 Transmission Reflection Example Haze % L* a* b* % L* a* b* 190.09 84.5 93.7 −1 4.4 15.1 45.7 0.6 −12.3 20 0.2 82.5 92.8 −1 5.3 16.347.4 0.6 −13.1 21 0.13 82.9 93 −1 5.1 15.8 46.7 0.6 −12.8 22 0.22 82.692.9 −1 5.3 17 48.2 0.5 −13.4 23 0.21 79.8 91.6 −0.9 6.2 18.4 49.9 0.4−13.7 24 0.45 81.1 92.2 −0.9 5.4 17.6 49 0.2 −12.6

Tin concentration within the titania coatings was measured using XPSdepth profiling for some Examples and the results are described in Table10 for particular delivery rates of tin chloride.

TABLE 10 TiO₂ Surface Tin Bulk Tin Thickness Concentration ConcentrationExample (Å) (atom %) (atom %) 17 119 0.8 0.1 20 207 0.9 0.1 15 215 1.10.2 23 259 2.1 0.4 24 283 4.3 1.2

Tin was found to be segregated at the top surface with lower levels oftin present in the body of the TiO₂.

EXAMPLES 25 TO 59 AND COMPARATIVE EXAMPLES A TO D

Examples 25 to 59 and Comparative Examples A to D were deposited by online CVD during the glass production process as described above inTable 1. Tin chloride was used as the tin precursor in Examples 25 to40, DMT as the tin precursor in Examples 41 to 59. No tin precursor wasused in the Comparative Examples. The specific coating conditions andvisible reflection for Examples 25 to 40 are described in Table 11, forComparative Examples A to D in Table 12 and for Examples 41 to 59 inTable 13. In each of the Examples 25 to 59 and Comparative Examples A toD, the nitrogen make up was 10 l/min.

TABLE 11 N₂ to N₂ to TiCl₄ EtOAc N₂ to SnCl₄ EtOAc:TiCl₄ VisibleExamples (cc/min) (cc/min) (cc/min) Ratio Reflection (%) 25 175 130 10 325.15 26 175 130 30 3 26.21 27 175 130 50 3 25.92 28 175 130 70 3 26.4129 175 130 100 3 26.51 30 175 210 100 5 23.5 31 175 210 70 5 23.58 32175 210 50 5 23.71 33 175 210 30 5 23.55 34 175 210 10 5 22.69 35 175175 10 4 24.42 36 175 175 30 4 25.3 37 175 175 50 4 25.61 38 150 150 304 21.16 39 125 125 30 4 19.2 40 175 90 30 2 29.47

TABLE 12 Comparative EtOAc:TiCl₄ Visible Examples N₂ to TiCl₄ N₂ toEtOAc Ratio reflection (%) A 250 170 3 19.26 B 250 280 5 17.2 C 250 1102 26 D 175 175 4 13.79

TABLE 13 Visible N₂ to EtOAc:TiCl₄ reflection Examples N₂ to TiCl₄ EtOAcN₂ to DMT Ratio (%) 41 175 130 10 3 14.67 42 175 130 30 3 19.13 43 175130 50 3 19.48 44 175 130 70 3 19.21 45 175 130 100 3 18.9 46 175 210100 5 16.76 47 175 910 70 5 17.9 48 175 210 50 5 18.54 49 175 210 30 519.29 50 175 210 10 5 18.7 51 175 90 10 2 23 52 175 90 30 2 23.5 53 17590 50 2 23 55 175 90 100 2 22.14 56 175 175 30 4 20.36 57 175 175 50 420.13 58 175 175 70 4 20.05 59 175 130 260 3 18

The coated glasses of Examples 24 to 59 and Comparative Examples A to Dwere tested for durability using the European surface #1 abrasion test(i.e. European standard abrasion test). Coatings were abraded for 500strokes and t_(90%), and the static water contact angle (to determinethe hydrophilic nature of the surface) were measured before and afterabrasion and the coatings were examined visually after abrasion.

Values of t_(90%) before and after abrasion and contact angle before andafter abrasion (the values after abrasion are in brackets) together withthe results of visual examination (visual) and examination as to thehydrophilicity (hydro) after abrasion of the coatings for Examples 25 to40 are described in Table 14, for Comparative Examples A to D in Table15 and for Examples 41 to 59 in Table 16. The static water contactangles were determined after exposure to sunlight for 24 hours. Theresults of visual examination and examination as to the hydrophilicityof the coatings after abrasion are reported in accordance with the key:Visual, 1=No Damage, 2=Damage, 3=Coating Removed; hydrophilicity,1=hydrophilic, 2=slightly patchy, 3=patchy, 4=fail.

TABLE 14 Abrasion Contact Angle Result t_(90%) before and (after) beforeand (after) Examples Visual Hydro abrasion abrasion 25 2 1 12.1 (19.7)26 1 1  72 (121)  5.4 (14.4) 27 1 1  69 (73)  6.4 (6.4) 28 1 1  76 (177)12.4 (21.4) 29 1 1  84 (43)  3.4 (24.1) 30 1 2 121 (200)   8 (6.2) 31 11  90 (97) 22.2 (17.7) 32 1 1  67 (127)  7.2 (24.5) 33 1 1  94 (132) 5.4 (5.4) 34 1 2  42 (95)   8 (11.5) 35 1 1  84 (889) 13.5 (19.5) 36 11  47 (103)   3 (3) 37 1 1  58 (97)  6.6 (5.8) 38 1 1 130 (128) 33.2(14.9) 39 1 1  68 (91)  1.8 (8.4) 40 1 1 134 (1109)  3.7 (12.5)

TABLE 15 Compara- Abrasion Contact Angle tive Result t_(90%) before and(after) before and (after) Examples Visual Hydro abrasion abrasion A 2.54  11 (2210)  5.7 (26) B 2.5 2  91 (1430)  3.4 (24.5) C 2.5 1  17   8(28.4) D 2.5 2 114 10.4 (18.4)

TABLE 16 Abrasion Contact Angle Result t_(90%) before and (after) beforeand (after) Examples Visual Hydro abrasion abrasion 41 1 1   43 (1275)11.6 (8.1) 42 1 1   41 (1169)  9.9 (10.6) 43 1 3   38 (160) 13.7 (23.9)44 1 1   40 (220) 14.7 (7) 45 1 1   38 (27)  4.6 (15.9) 46 1 1   39 (32)10.2 (10.2) 47 1 1 54.5 (188)  6.3 (6) 48 1 1   42 (39) 11.9 (14.5) 49 11   50 (1085) 15.1 (14.4) 50 1 1   76 (1055) 27.9 (20.9) 51 2 2   19(975) 33.2 (21.6) 52 1 1   30 (1095)  5.4 (18.1) 53 1.5 1   90 (31) 18.6(26.4) 55 1 1   32 (295)  9.9 (8.4) 56 1 1   42 (2350) 15.1 (11.5) 57 11   51 (82)  7.8 (6.7) 58 1 1   86 (1110) 17.5 (17.3) 59 1 3   38 (99)10.4 (26)

XPS analysis of the tin containing coatings indicated tin segregation atthe surface of the coating with a lower tin content measured in the bulkof the titania coating. This was observed with both SnCl₄ and DMT.Summary measurements are shown in Table 17 below.

TABLE 17 Surface tin Bulk tin Tin Precursor flow EtOAc:TiCl₄concentration concentration rate Molar Ratio (atom %) (atom %) 0.12g/min SnCl₄ 3:1 0.4 to 0.9 0.1 0.28 g/min SnCl₄ 3:1 0.7 to 1.2 0.1 to0.3 0.28 g/min SnCl₄ 5:1 0.6 to 1.2 0.1 to 0.4 0.12 g/min DMT 3:1 0.8 to1.5 0.1 to 0.3

EXAMPLES 60 TO 66

Examples 60 to 66 were deposited by on line CVD during the float glassproduction process across the full width of a float glass ribbon asdescribed above in Table 2. DMT was used as the tin precursor. The flowrates of DMT used for each of the Examples 60 to 66 are described inTable 18, together with values of t_(90%) and static water contact anglebefore and after 500 abrasion strokes in accordance with the Europeanstandard abrasion after abrasion are in brackets).

TABLE 18 Contact Angle DMT flow t_(90%) before and (after) before and(after) Example (cc/min) abrasion abrasion 60 2.5 30 (1240) 21.1 (21.1)61 5 51 (1240) 14.7 (13) 62 7.5 31 (560)  6.7 (8.2) 63 10 25 (2540)  7.9(13.1) 64 12.5 87 (1240)  6.4 (6.6) 65 15 70 (1280)   16 (16) 66 20 50(1630) 20.3 (17.5)

t_(90%) was measured after the coatings were exposed to sunlight for 24hours.

Examination by scanning electron microscopy (SEM) showed that afterabrasion, coatings with no tin were highly furrowed and many parallelabrasion marks were scored into the surface of the coating. There wasalso a small loss in coating thickness. By comparison tin containingcoatings were marked less, there was no significant loss in thickness,and the coating surface appeared smooth.

The optical properties of the coatings were investigated before andafter abrasion. The visible transmission and transmission colours of theExamples 60 to 66 are described in Table 19, the visible reflection andcolours in reflection are described in Table 20 (in Table 19 and Table20 the values after abrasion are in brackets).

TABLE 19 Visible Transmission L* before and a* before and b* before andbefore and (after) (after) abrasion (after) abrasion (after) abrasionExample abrasion (%) (transmission) (transmission) (transmission) 6085.8 (85.2) 94.2 (94) −1.1 (−1.1)   3 (3) 61   86 (85.6) 94.3 (94.1)−1.1 (−1.1) 2.9 (2.7) 62 84.1 (83.8) 93.5 (93.3) −1.1 (−1.1) 3.7 (3.6)63 84.8 (84.6) 93.8 (93.7) −1.1 (−1.1) 3.4 (3.2) 64 84.6 (84.7) 93.7(93.8) −1.1 (−1.1) 3.6 (3.2) 65 85.1 (84.3) 93.9 (93.6) −1.1 (−1.1) 3.4(3.4) 66 84.1 (83.9) 93.5 (93.4) −1.1 (−1.1) 3.8 (3.6)

TABLE 20 Visible Reflection L* before and a* before and b* before andbefore and (after) (after) abrasion (after) abrasion (after) abrasionExample abrasion (%) (reflection) (reflection) (reflection) 60 13.3(13.1) 43.2 (43) 0.4 (0.3)   −10 (−8.7) 61 12.6 (12.9) 42.2 (42.6) 0.4(0.3)  −8.4 (−8.1) 62 14.9 (15.2) 45.4 (45.9) 0.4 (0.4) −11.2 (−10) 63  14 (13.8) 44.2 (44) 0.3 (0.3) −10.4 (−8.9) 64   14 (14.1) 44.2 (44.4)0.4 (0.4) −10.6 (−9.3) 65 13.8 (14.1)   44 (44.4) 0.3 (0.3) −10.8 (−9.3)66 14.9 (14.8) 45.5 (45.3) 0.3 (0.4) −11.3 (−9.8)

The coatings were analysed by XPS profiling and the results of XPS ofthe thickness of the silica undercoat and the titania layer, togetherwith the surface and bulk elemental analyses for tin and carbon, aredescribed in Table 21.

TABLE 21 SiO₂ Surface Bulk Undercoat TiO₂ Composition CompositionThickness Thickness (atom %) (atom %) Example (Å) (Å) Sn C Sn C 60 293242 0.2 34.0 0.07 8.7 61 293 220 0.3 11.6 0.12 2.8 62 293 242 0.5 18.00.06 2.6 63 293 242 0.4 16.9 0.05 1.4 64 297 255 0.5 47.1 0.13 11.2 65300 242 0.6 17.3 0.12 1.7 66 375 352 0.5 33.2 0.13 8.2

1. A process for the production of a durable photocatalytically activeself-cleaning coated glass comprising contacting the surface of a hotglass substrate with a fluid mixture comprising titanium chloride asource of oxygen and a tin precursor thereby depositing a tin containingtitanium oxide coating on the surface of the glass substrate whereinthere is a greater atomic percent tin in the surface of the tincontaining titanium oxide coating than there is in the bulk of thecoating.
 2. A process as claimed in claim 1 wherein at least part of thefluid mixture contacts the surface of the glass substrate by flowingover the glass surface.
 3. A process as claimed in claim 1 whereintitanium chloride comprises titanium tetrachloride.
 4. A process asclaimed in claim 1 wherein the tin precursor comprises a tin halide. 5.A process as claimed in claim 4 wherein the tin halide comprises a tinchloride.
 6. A process as claimed in claim 5 wherein the tin chloridecomprises dimethyl tin dichloride or tin tetrachloride.
 7. A process asclaimed in claim 1 wherein the source of oxygen comprises an ester.
 8. Aprocess as claimed in claim 7 wherein the ester comprises a carboxylicacid ester.
 9. A process as claimed in claim 8 wherein the carboxylicacid ester comprises a C₁ to C₄ acetate.
 10. A process as claimed inclaim 9 wherein the C₁ to C₄ acetate comprises ethyl acetate.
 11. Aprocess as claimed in claim 1 wherein the glass substrate comprises asoda-lime-silicate glass substrate.
 12. A process as claimed in claim 11further comprising depositing an alkali blocking underlayer on thesurface of the glass substrate before depositing the tin containingtitanium oxide coating.
 13. A process as claimed in claim 1 wherein thefluid mixture comprises a gaseous mixture.
 14. A process as claimed inclaim 1 wherein the hot glass substrate is at a temperature in the range500° C. to 750° C.
 15. A process as claimed in claim 14 wherein the hotglass substrate is at a temperature in the range 570° C. to 650° C. 16.A process as claimed in claim 1 wherein the process is performed duringthe float glass production process.
 17. A process as claimed in claim 16wherein the process is performed in the float bath.
 18. A process asclaimed in claim 1 wherein the amount of tin in the bulk of the tincontaining titanium oxide coating is below 10 atom %.
 19. A process asclaimed in claim 18 wherein the amount of tin in the bulk of the tincontaining titanium oxide coating is below 5 atom %.
 20. A process asclaimed in claim 19 wherein the amount of tin in the bulk of the tincontaining titanium oxide coating is below 2 atom %.
 21. A process asclaimed in claim 1 wherein the atomic percent tin in the surface of thetin containing titanium oxide coating is at least twice that in the bulkof the coating.
 22. A process according to claim 1 wherein the amount oftin in the bulk of the tin containing titanium oxide coating is below 10atomic percent.
 23. A durable photocatalytically active coated glasscomprising a glass substrate having a coating comprising tin containingtitanium oxide, the amount of tin in the bulk of the coating being below10 atomic percent and the atomic percent tin in the surface of thecoating is at least twice that in the bulk of the coating.
 24. A durablephotocatalytically active glass according to claim 23 wherein the atomicpercent tin in the surface of the coating is above 0.05%.
 25. A durablephotocatalytically active glass according to claim 23 wherein the amountof tin in the bulk of the coating is in the range of 0.05 atomic percentto 5 atomic percent.